Two-wire multiple automatic telephone system



B. G. DUNHAM.

TWO WIRE MULTIPLE AUTOMATIC TELEPHONE SYSTEM.

APPLlCATlON FILED AUG=30, I915 1,339,175, Patented May 4,1920.

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B. G. DUNHAM.

TWO WIRE MULTIPLE AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED AUG-30,1915.

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TWO WIRE MULTIPLE AUTOMATIC TELEPHONE SYSTEM.

APPLICATION FILED Aueiao. 1915.

Patented May 4, 1920.

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BERT G. DUNHAM, OF HAWTHORNE, NEW JERSEY, ASSIGNOR, BY MESITE ASSIGN- MENTS, T0 WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK.

Specification of Letters Patent.

Patented May 4, 1920.

Application filed August 30, 1915. Serial No. 48,134.

To all whom it may concern:

Be it known that I, BERT G. DUNHAM, a a

citizen of the United States, residing at Hawthorne, in the county of Passaic and State of New Jersey, have invented certain new and useful Improvements in Two-Wire Multiple Automatic Telephone Systems, of

-which the following is a full, clear, concise,

and exact description.

This invention relates to improvements in an automatic telephone system of the twowire multiple type, such as shown in an application of Charles L. Goodrum, Serial No. 35,326, filed June 21, 1915 issued as Patent No. 1,251,503, Jan. 1, 1918.

One of the objects of this invention is the provision of a system, in which the bridges containing the operating relays are not re moved'from the line after the establishment of a connection.

Another object of the invention is the .provision of a repeating relay at a selector switch by means of which the controlling impulses for operating the succeeding switches are relayed over one of the talking conductors.

Figures 1, 2 and 3 of the drawings, with Fig. 1 at the left and Figs. 2 and 8 following in order, show the circuits of the invention and diagrammatically indicate the apparatus employed therein.

Any step-by-step two-movement switch may be employed with the circuits shown. A switch of this general character is shown in a patent to Keith and, Erickson No. 815,175, although a switch such as disclosed in an application of Charles L. Goodrum, Serial No. 872,748, filed November 18, 1914, will preferably be employed. Of course, it is to be understood that in practising this invention only two brushes will be employed on each switch, and the stationary contacts will be correspondingly reduced in number.

Although the invention is disclosed in a system using 'step-by-step switches, certain features thereof are applicable to systems employing other types, as power-driven switches.

lVith each switch is associated a circuitchanging device for controlling certain op erating circuits at its respective switch. These devices may be of the general character of the switch shown in the above mentioned patent and referred to therein as a side switch. A circuit controlling switch, such as Wlll preferably be employed in the "present invention, is shown in the above mentioned Goodrum application. Such a circuit controlling device may be caused to effectcircuit changes, either b the deenergization or the energization 0 its operztrting magnet as described in said applica- The line finder switch and circuits shown on Flg. 1 are substantially the same as disclosed in the Goodrum application above referred to, and, therefore, this part of the system will be only briefly described.

As the, circuits employed in this system are of a very simple character, it is believed that the invention will be readily understood from the following description in which the establishment of a successful and an unsuccessful connection is described, and also the manner of releasing the switches in either instance.

We will assume that the subscriber shown at the left in Fig. 1 of the drawings desires to establish a connection with the subscriber shownto the right in Fig. 3. Uponremoving his receiver from the hook, a circuit is completed through line relay 1 which, in attracting its armature, completes a circuit from battery through relay 2, left back contact of relay 3, left back contact of test relay 4, left contact of relay 1, and right winding of relay 1 to ground. Relay 2 pulls up and completes a locking circuit through its left armature. A circuit is now completed from battery through rotary stepping magnet 5, side switch wiper 6, back contact of release magnet 7, relay 3, innermost right armature and front contact of relay 2, and right armature of relay 4 to ground. Due to the individual interrupter associated with the magnet 5, the switch brushes are moved from group to group of the line contacts until the rotary test brush 8 engages the contact individual to the group of the calling line, when a circuit is completed from battery through escape or side switch magnet 9, side switch wiper 10, brush 8, to the group contact of the calling line, armature and contact of relay 2, and armature and contact of relay 4 to ground. The escape magnet 9 operates and moves the side switch wipers to position 2.

In position 2, a circuit is completed from battery through vertical stepping magnet 11, side switch wiper 6, contact and armature of release magnet 7 to ground at the right armature of relay 4. The switch brushes 12 and 13 are stepped from line to line until the terminals of the calling line are encountered, when a circuit will be completed from a source of current through test relay 4, right front contact of line relay 1 the upper talking conductor of the line, line contact and brush 13, side switch wiper 14, the lower trunk conductor, condenser 15 and resistance 16 to battery and ground. Test relay 4 is energized and removes the ground from the vertical stepping magnet circuit, thus stopping the movement of the switch. The escape magnet 9 was energized 1n parallel with the vertical magnet 11. Upon the operation of relay 4, it becomes de'e'nergized, moving the side switch wipers to position 3.

The calling line is now connected through the side switch wipers 14 and 17 to the first selector switch. A circuit now extends from battery through resistance 16, the lower trunk conductor, side switch wiper 17, brush 12 and cut-off relay 18 to ground. Belay 18 is operated and removes the subscribers line from connection with the line relay 1.

V hen side switch wiper 17 moves into the third position, busy potential is supplied to the multiple contacts associated with the brush 12 through resistance 16. The apparatus is now in condition for the receipt of the controlling impulses at the first selector shown at the left in Fig. 2.

The calling subscriber now works his dial to operate the line relay 19 at the first selector. The operating circuit may be traced from battery through resistance 16, the lower trunk conductor, left side of the calling subscribers line, the substation and the calling device thereat, the right side of the subscribers line, upper trunk conductor and through relay 19 to ground. Upon the first energization of relay 19, a circuit is completed from ground, armature and front contact of said relay, rotary off-normal contact 20, back contact of rotary stepping magnet 21, side switch wiper 22 and the escape magnet 23 to battery and ground. The escape,

magnet is made slow to release, and consequently holds up during the series of impulses. On the first deenergization of the line relay, a circuit is completed from ground through its armature and back contact, armature and front contact of escape magnet 23, side switch wiper 24, and rotary magnet 21 to battery and ground. The rotary magnet is energized with each deenergization of the line relay l9. \Vith the first rotary step, the rotary off-normal contact spring 20 separates from its upper contact and engages its lower contact, and through the remaining impulses of the series the magnet 23 is maintained energized at the back contact of relay 19. At the termination of the series of impulses, relay 19 remains energized and the escape magnet 23 falls off, moving the side switch wipers to position 2' A circuit now extends from battery through vertical stepping magnet 26, side switch wiper 25, back contact of test relay 27 and front contact of line relay 19 to ground. The brushes 28 and 29 are moved from trunk to trunk by the repeated energization and deene-rgization of the ma net 26 brought about by means of its individual interrupter 30. hen the contacts of an idle trunk of the group are encountered, a circuit is completed from battery through test relay 27, brush 29. conductor 31, rotary offnormal contact 32, back contact of escape magnet 33, and back contact of line relay 34 to ground. Relay 27 is energized and inter-' rupts the circuit for magnet 26, thus stopping the movement of the brushes and closes a circuit from battery through escape magnet 23, wiper 22, front contact of relay 27, and front contact of relay 19 to ground. Magnet 23 is energized and causes the side switch wipers to move into position 3.

In position 3, circuits are completed for line relay 34 and for relay 36 as follows: from battery through relay 34, brush 28, side switch wiper-37, back contact of relay 36 to ground, through front contact and armature of relay 19. Another circuit is completed from battery through relay 36, side switch wiper 38, front contact of test relay 27 to ground through contact and ar mature of relay 19. As relay 36 is made slow to pull up, relay 34 becomes energized and interrupts the circuit for test relay 27, which falls off before relay 36 has attracted its armature. Upon the energization of relay 34, a circuit is completed from battery through relay 33, side switch wiper 39, contact and armature of rotary stepping magnet 40, rotary off-normal contact 41, and front contact and armature of relay 34 to ground. Relay 33 energizes, and as it is made slow to release it remains energized throughout the series of impulses.

Ve are now ready for sending the impulses to the second selector switch. The impulses for the second selector switch and the connector are relayed by means of line relay 19. Upon sending the impulses, the relay 19 is repeatedly energized and deenergized as occurred when the first selector switch was operated. Upon each energization of said relay, a circuit is completed from ground through armature and front contact of relay 19, back contact and armature of relay 36, and line relay 34 to battery and ground. Thus relay 34 will be energized with each energization of relay 19 and through rotary stepping magnet 40, side switch wiper 45, front contact and armature of relay 33, and back contact and armature of relay 34, to ground. Thus, by means of the impulses transmitted from the calling subscribersstation, the brushes 47, 48 are stepped from group to group of the trunks leading to final connectors, such as shown in Fig. 3. With the first rotary impulse, the oif-normal contact 41 opens at its upper contact and closes at its lower one, so throughout the succeeding impulses of the series the relay 33 is maintained energized at the back contact of rela' 34. At the termination of this series 0 impulses, the relay 34 remains energized and the relay 33 falls off and interrupts the previousl established circuit from battery throu escape magnet 42, wiper 43, wiper 51, rig 1t contact of relay 33, and back contact of relay 35. Magnet 42 retracts its armature and moves the side switch wipers into position 2.

A circuit is now completed from battery through the vertical stepping magnet 49, its individual interrupter contact 50, wiper 51, front contact and armature of relay 33, and back contact and armature of relay 35 to ground, relay 33 having been energized by the closure at wiper 39 in its second position of the following circuit; grounded battery, relay 33, wiper 39, front contact and armature of relay 34 to ground. By means of its individual interrupter, the magnet 49 is repeatedly energized and deenergized, thus stepping the switch brushes over the busy trunks of the group with which they are now associated.

When an idle trunk is found, a circuit is completed from battery through test relay 35, the upper trunk conductor, conductor 52, rotary off-normal contact 53, back contact and left armature of relay 54, and back contact and armature of relay 55 to ground. Relay is energized and interrupts the circuit for the "ertical stepping magnet 49. It also closes a circuit from battery through the escape magnet 42 and wiper 43, and the side switch wipers move to position 3.

\Vheu the side switch moves to position 3, a circuit is completed from battery through line relay 55, lower trunk conductor, side switch wiper 44, wiper 37, armature and back contact of relay 36 to ground, through front contact and armature of relay 19. Relay in pulling up interrupts the circuit for the test relay 35, which becomes deenergized. A circuit is also completed from battery through slow-release relay 54, side switch wiper 58, armature and contact of rotary magnet 59, rotary off-normal contact 60, and front contact and armature of relay to ground. The energization of relay 54 completes a circuit from battery through slow-release escape magnet 61, contact and right armature of relay 54, back contact and armature of relay 62, and back contact and armature of relay 63 to ground.

The subscriber now works his sending device, causing the repeated energization and deenergization of line relay 19, which, as before, grounds the lower side of the line with each energization and removes said ground with each deenergization. With each deenergization of relay 19, relay 55 becomes deenergized and completes a circuit from battery through rotary stepping magnet 59, wiper 64, front contact and armature of'relay 54, and back contact and armature of relay 55 to ground. The connector switch brushes are, therefore, stepped from group to group of the contacts of the lines terminating therein. With the first rotary impulse, contact 60 separated from its uppercontact and engaged its lower one, and through the remaining impulses of the series the relay 54 is maintained energized through said off-normal contact 60 and back contact of relay 55. r

Upon the termination of the impulses of the series, however, relay 54 becomes deenergized and in turn interrupts the circuit for the escape magnet 61, causing the side switch to move to position 2. A circuit now extends from battery through relay 54, wiper 58, armature and contact of magnet 65, vertical off-normal contact 66, front contact and armature of rela 55 to ground. The units series of impu ses are now transmitted by the calling subscriber, causing the repeated energization and deenergization of the relay 55 in a manner now well understood. With each deenergization, a circuit is completed from battery through vertical stepping magnet 65, side switch wiper 64, front contact and armature of relay 54, back contact and armature of relay 55 to ground. With the first vertical step, contact spring 66 disengages its upper coiiperating contact and engages its lower one, and throughout the remaining impulses of the series the relay 54 is maintained energized through the back contact of relay 55.

When the switch brushes stop on the terminals of the desired line, a circuit is completed from ground through right winding of relay 67, back contact and armature of relay 68 to the lower connector switch brush and contact engaged thereby. If the called line is busy, battery potential will be upon this contact. If the line is busy as a calling line, this current will be supplied through resistance 16 at the first selector. If busy as a called line, the busy potential will be supplied through relay 68 at the connector position 3, thus completing a circuit from ringing trip relay 62,

responds, relay 62 will become energized due to the increased flow of current.

When the side switch went to position 3, a

- circuit was completed from battery through relay 54, side switch wiper 58, and front contact and armature of relay 55 to ground.

Relay 54 in turn completed a circuit from battery through escape magnet 61, contact and armature of relay 54, back contact and armature of relay 62 to ground, through contact and armature of relay 63. When the triprelay 62 attracts its armature, it interrupts the last traced circuit causing the side switch to move to position 4.

In position 4, a circuit is completed from ground through left winding of relay 67, side switch wiper 71, conductor, 52, upper trunk conductor and relay 27 to battery and ground. Relay 27 pulls up and completes a circuit from battery through relay- 36, wiper 38, front contact of relay 27, and front contact of relay 19 to ground. Relays 67 and 36 being. energized, the connection is now complete through to the line of the called subscriber. When relay 27 was energized, relay 35 also became energized over a parallel circuit and completed a circuit from battery through relay 33 and wiper 39. This holds relay 33 energized and the circuit for release magnet 73 open.

The release of the finder switch and first selector switch is now under the control of the'calling subscriber, while the release of the second selector switch and the connector switch is under the control of the called subscriber. When the side switch moved into position 4, relay 63 was energized by current supplied over the subscribers line from battery at relay 68. Relay 63 in turn completed a circuit from battery through relay 54, wiper 58 and the armature and contact of .relay 63. Therefore, the circuit of the release magnet 72 is maintained open at the left armature and back contact of relay 54 as long as thecalled subscribers circuit is closed. The circuit for the release magnet 73 of the second selector is maintained open at the back contact of relay 33.

When the called subscriber replaces his receiver on the hook, relay 63 becomes deenergized and interrupts the circuit for relay 54. Relay 54 retracts its armature and completes a circuit from battery through means release magnet '72, off-normal contact 53, back contact and armature of relay 54, and back contact and armature of relay 55. Relay 55 was dee'nergized when relay 36 pulled up and removed fiound from. the lower trunk conductor. agnet 72 upon energization closes a locking circuit for itself through its armature 74, so that it will be maintained energized until off-normal contact 53 is opened when the switch reaches its normal position.

As the side switch returns to its normal position wiper 71 removes ground from the upper trunk conductor, causing relay 35 to become deenergized. This interrupts the circuit of relay 33, which falls oil and closes a circuit from battery through the winding of release magnet 73, off-normal contact 32, back contact and armature of relay 33, and back contact and armature of relay 34. Re? lease magnet 75 is energized and completes a locking circuit for itself in the same way as did magnet 72.

Turning now to the first selector, it will be noted that the slow-release magnet 23 has been maintained energized during conversation, and indeed at all times since the side switch wiper went into the third position, by a circuit extending through the front contact of relay 19. Now when the calling subscriber replaces his receiver upon the hook, the circuit for relay 19 is interrupted and it releases its armature, thus interrugting the circuit for the magnet 23 whic retracts its armature. Circuits are now completed from battery through the release magnets 7 and 75 in parallel through the rotary oif-normal contact 76, back contact and armature of relay 23, back contact and armature of relay 19 to ground. Release magnets 7 and 75 are energized and return the finder switch and the first selector switch to their normal positions.

We will now consider an unsuccessful call. It will be remembered that at the time the connector switch brushes made connection with the terminals of the wanted subscribers line, the side switch was in position 2. If the line is busy, the lower or test terminal of the line in Fig. 3 will be of raised potential, as hereinbefore described, and current will flow from said terminal through the lower switch brush, armature and back contact of relay 68, and the right windin of relay 67 to ground, energizing relay 6 As the escape magnet 61 is slow to release, it has held up during this operation, and a holding circuit is now provided therefor which extends through side switch wiper 69, contact and left armature of test relay 67, side switch wiper 71 and the left Winding of relay 67, thus maintaining the side switch in position 2. Relay 67 at its right armature and front contact connects the busy tone device 77 to the upper conductor of the trunk, thus causin a tone to be transmitted to the calling su criber to indicate to him that the wanted line is busy. Relay 68 will be energized by a circuit extendin through the contact and left armature 0 relay 67, wiper 71 and left winding of relay 67; but as the side switch is still in position 2, the rin ing. circuit will be open at side switch wiper 70. The calling subscriber hearing the busy tone will replace his receiver on the hook, causing the release of the finder switch and the first selector in the manner hereinbefore described. When relay 19 retracts its armature, ground will be removed from the lower trunk conductor, and relays 34 and 55 will become deenergized.

As relay 35 is deenergized at this time, the energizing circuit for relay 33 is controlled at the front contact of relay 34. Therefore when relay 34 retracts its armature, relay 33 also falls off, and a circuit is completed from battery through release magnet 73, offnormal contact 32, back contact of relay 33 and back contact of relay 34. Magnet 73 pulls up and completes a locking circuit for itself as before described. The armatures of relay 54 will be back at this time, and when relay 55 retracts its armature a circuit will be completed from battery through release magnet 72, off-normal contact 53 and back contacts of relays 54 and 55, causing magnet 72 to pull up and lock. When relay 55 retracted its armature, it also completed a circuit for relay 54, but magnet 72 will have operated and locked up before relay 54 will open the energizing circuit therefor.

Associated with each of the stepping magnets of the selector switches and of the connector switch, by means of which directive movement is imparted to said switches, is an armature contact device, by means of which the switch is prevented from being tied up if the calling; subscriber replaces his receiver on the hool pulses are being tran ;.;:.nitted.

Referring first to the first selector (at the left in Fig. 2), it will be remembered that at the time the series of impulses are transmitted to effect the rotary movement of this switch, the side switch is in position 1. If now, after a certain number of impulses have been transmitted, but before the switch has had time to hunt for and select an idle trunk in the selected group, the substation circuit of the calling subscriber is interrupted, the line relay 19 will retract its armature and will remain back. After the first rotary step, the escape magnet 23 is maintained energized by a circuitextending through side switch w1per 22, contact and armature of rotary magnet 21, off-normal contact spring 20 and its lower contact, and the back ,contact of line relay 19. Thus it will be seen that if it were not that this cirwhile a series of imcuit was carried through the armature of stepping magnet 21, the escape ma et would remain energized and the switch would, therefore, be tied up. However, when the line relay retracted its armature, 1t completed a circuit for the rotary magnet 21, as previously described, causing it to open and maintain open the circuit of the escape magnet 23, which, after a brief interval, would fall off and complete the circuit for the release magnet 75. The same provis on is made at the second selector, and it 1s thought its operation will be readily understood from the foregoing description.

A similar expedient is also employed in association with both the stepping magnets of the connector switch, and it is thought that the manner in which the release is effected in the connector will also be readily understood from the description ofthe release of the first selector switch.

It will be noted that in the present system there is a portion of the talking circuit included between the condensers at the left in F g. 2 and those at the left in Fig. 3 over one of the conductors of which the repeatmg 1m ulses are transmitted from the relay 19, an over the other of which the test is accomplished. This permits the provision of operating circuits wherein the relays and magnets associated with the conductors in establishing a connection need not be cut off during conversation, as it has been found that if the relays branched off from the con ductors included between the condensers before mentioned are of relatively high resistance and impedance, the loss of voice currents is so slight as to be negligible.

In the present system, it will be noted that the operating impulses for the stepping relays are transmitted over one of the talking conductors, and that the release and the test, with the exception of that of the connector,

takes place over the other talking conductor.

It is obvious that many modifications of the present invention may be devised without departing from the spirit thereof. Applicant therefore desires it understood that the invention is to be limited merely by the scope of the claims.

What is claimed is:

1. In a telephone exchange system, a selector switch, conductors extending to said switch, means for receiving selecting impulses sent according to a predetermined code joined to one of said conductors, a source of current, and a testing device at said switch permanently connected to said source and to the same conductor.

2. In a telephone exchange system, a selector switch, conductors extending to said switch, means for receiving selecting impulses sent according to a predetermined code joined to one of said conductors, and

a testing device at said switch connected to an inductively associated portion of the same conductor.

3. In a telephone exchz nge system, a selector switch, conductors lextending to said switch, means for transmitting impulses over said conductors to said switch, impulse receiving means connected to one of said conductors and arranged to be operated by every impulse transmitted over said conductors, release means controlled by said impulse receiving means, and test means con-- nected to the same conductor.

4. In a telephone exchange system, a selector switch, talking conductors extending to said switch, means for transmitting impulses over said talking conductors to said switch, impulse receiving means connected to one of said talking conductors and arranged to be operated by every impulse transmitted over said talking conductors, re-

lease means controlled by said impulse receiving means, and test means connected to the same talking conductor.

5. In a telephone exchange system, a selector switch, talking conductors extending thereto, test means permanently connected to one of said talking conductors, and release means connected to the same conductor.

6. In a telephone exchange system, a

switch, a pair of conductors extending to said switch, a stepping relay permanently source and the other said conductor, said controlling relay being arranged to also determine the busy or idle condition of the wanted line.

8. In a telephone exchange system, a switch, a pair of conductors extending thereto, means for transmitting impulses over said conductors to said switch, a stepping relay oonnected to one of said conductors and arranged to be operated by every impulse transmitted over said conductors,

releasing means controlled by said stepping relay, and a test relay connected to the same conductor.

9. In a telephone system, a connector or final switch, a pair of talking conductors at said switch for controlling the setting thereofpermanently joined to one of said conductors, a second relay, through which talking current is supplied to the called subscriber, permanently joined to the other said conductor, release means for said switch controlled by, said stepping relay prior to 11. In a telephone exchange system, a

switch, a pair of conductors extending thereto, means for transmitting impulses over said conductors tosaid switch, a stepping relay connected to one of said. conductors and arranged to be operated by every impulse transmitted over said conductors, a test relay connected to the same conductor, and a release controlling means connected to the other conductor.

12. In a telephone exchange system, a switch, a pair of talking conductors extending thereto, means for transmitting impulses over said talking conductors to said switch, a stepping relay connected to one of said talking conductors and arranged to be operated by every impulse transmitted over said talking conductors, a test relay connected to the same talking conductor, and a release controlling means connected to the other talking conductor.

In witness whereof I hereunto subscribe my name this 26th day of August, A. D.

BERT G. DUNHAM. 

